1. Selenium is pure open source, freeware and portable tool.
2. Selenium supports variety of languages that include Java, Perl, Python, C#, Ruby, Groovy, Java Script, and VB Script. etc.
3. Selenium supports many operating systems like Windows, Macintosh, Linux, Unix etc.
4. Selenium supports many browsers like Internet explorer, Chrome, Firefox, Opera, Safari etc.
5. Selenium can be integrated with ANT or Maven kind of framework for source code compilation.
6. Selenium can be integrated with TestNG testing framework for testing our applications and generating reports.
7. Selenium can be integrated with Jenkins or Hudson for continuous integration.
8. Selenium can be integrated with other open source tools for supporting other features.
9. Selenium can be used for Android, IPhone, Blackberry etc. based application testing.
10. Selenium supports very less CPU and RAM consumption for script execution.
11. Selenium comes with different component to provide support to its parent which is Selenium IDE, Selenium Grid and Selenium Remote Control (RC).